RV sofa bed mattress: why nothing off the shelf fits, and what to do
As an Amazon Associate I earn from qualifying purchases. What that means.
Quick answer
The second bed in most coaches is a cushion cut to the sofa, not a mattress in a size anybody sells. Plan on Trim to fit 24 x 72 x 4-6 foam trimmed to your own measurements, choose firmness by ILD rather than by thickness, and measure the cavity with the bed folded closed before you order anything.
A jackknife sofa is the bed guests actually sleep on, and it is the one nobody plans for. The factory cushion is thin because it has to fold, it sits over a frame that telegraphs through, and the size is whatever the builder needed against that wall. There is no short queen equivalent here: the replacement is foam you cut.
Measure the cavity, not the cushion
The old cushion has been compressed for years and it has lost height. Measure the space the mechanism gives you with the bed closed and the frame at rest: width across the seat, depth front to back, and the vertical gap the cushion has to fold into. That vertical number is the ceiling on thickness, and exceeding it does not make a softer bed, it makes a sofa that no longer closes.
If the sofa is a hide-a-bed with a folding metal frame rather than a jackknife, measure the frame platform instead, and add the bar you can feel through the current mattress to the list of things a thicker cushion has to cover.
Firmness is the specification that matters
Upholstery foam is sold by ILD, which is the force it takes to compress it. A sofa cushion has two jobs that pull in opposite directions: hold a seated body on a small contact area for years, and spread a sleeping body across a whole night. Firmer wins on durability and on not bottoming out onto the frame; softer wins on the one night a guest stays. For a bed that gets used weekly, err firm and put a two-inch topper on it for sleeping.
Foam sheets worth cutting
Trim to fit 24 x 72 x 6 GoTo FoamUpholstery Cushion 44 ILD, 6 in
Six inches at 44 ILD, the firm end, and the option when the cushion has to carry seated weight every day rather than a guest twice a year. Sold as a sheet to trim: the figures come from the listing, since the brand has no specification page of its own.
Check size and availability(paid link)
Trim to fit 24 x 72 x 6 FoamTouchHigh Density Upholstery Foam, 6 in
Six inches of high-density foam in the same 24 by 72 sheet. Same caveat on the source of the numbers, same job: cut to the cavity, cover it, and the bar stops telegraphing.
Check size and availability(paid link)
Trim to fit 24 x 72 x 4 FoammaHigh-Density Upholstery Foam, 4 in
Four inches, for a mechanism that will not close on six. Thinner foam needs to be firmer to avoid bottoming out, which is the trade-off this thickness forces.
Check size and availability(paid link)
All three are listing-only: the dimensions are published where the product is sold rather than on a brand specification page. For foam sheets that is normal, and it is also why the measurement that matters is the one you take in the coach. How we test covers what each label means.
Cutting it without wrecking it
An electric carving knife is the tool. Mark the line on both faces, because a blade wanders through six inches of foam and a line on the top only tells you where you started. Cut slightly outside the line in one continuous pass and trim back rather than sawing to a perfect edge: foam compresses under pressure and springs back afterwards, so a slow cut ends up wavy in a way that shows once the cover goes on.
Keep the old cushion cover if it is sound. Re-covering is the part most people underestimate, and a zippered cover cut to the original size is worth more than the foam inside it.
When the sofa is not the answer
If the sofa bed is where somebody sleeps every night rather than occasionally, the cushion is the wrong problem to solve. A dinette conversion or a bunk gives a flat platform that takes a proper mattress, and both are covered in the size chart. A sofa bed is built to fold; comfort is what it trades away to do that.
Questions people ask
Can I buy a replacement mattress for an RV sofa bed?
Not as a stock size, in most coaches. Jackknife and hide-a-bed cushions are cut to the sofa, and the sofa is cut to the wall it sits against, so the practical route is a foam sheet trimmed to your measurements rather than a product that arrives ready to drop in.
What firmness should sofa bed foam be?
Firmer than a mattress. A sofa cushion carries seated weight on a small area all day and sleeping weight at night, so upholstery foam is rated by ILD, the force needed to compress it. A cushion that feels right to sit on will feel firm to sleep on, and that trade is the whole design problem of a sofa bed.
How thick can the foam be?
As thick as the mechanism folds. Measure the cavity with the bed closed, not the cushion you are replacing: a jackknife that swallows four inches will not close on six, and forcing it strains the frame rather than compressing the foam.
How do you cut foam cleanly?
An electric carving knife with a long blade, a straight edge, and a single pass per line. Mark both faces, cut slightly proud of the line and trim back. Foam compresses under a blade, so a slow saw cut wanders and a fast clean stroke does not.
Is a topper enough instead?
Sometimes, and it is the cheaper test. If the complaint is the bar across the middle or a thin cushion over a metal frame, two inches of foam on top changes the night for a fraction of the price. If the cushion has collapsed, a topper follows the collapse.
Sources
- Manufacturer specification pages for each product named, checked on the brand's own site where one exists
Last updated 2026-09-20